Pilot studies have been conducted in 7 baboons to evaluate the effect of blood CO2 tension on CSF absorption. Five of the 7 animals demonstrated a significant increase in CSF outflow resistance with increased CO2 tension. The exponential and linear models of CSF absorption have been compared in cats, baboons and in patients. These comparisons suggested certain modifications in the exponential model. The Starling Resistor Effect in the cerebral venous drainage has been studied in an electrical analog model to determine if it might help explain why plateau waves resolve rapidly in patients. Software and hardware have been developed to allow computer-controlled infusions of mock CSF in baboons.